This invention relates to an improved desoldering braid for use in removing solder from soldering joints, and to apparatus for use in the manufacture of such braid.
Solder-pulling wicks in the form of a desoldering braid have been in use for some time to remove solder from a soldered connection quickly and economically. Such wicks have been made of metal strands or wires braided to provide a capillary surface. Such wicks have generally been made of copper, in view of its heat-conducting properties. In some instances, flux is applied to the solder connection prior to contact with the wick in order to improve the wetting properties of the solder. Alternatively, desoldering braid has been provided with an overcoating of flux. Exemplary solder wicks are described in U.S. Pat. No. 3,627,191 to Hood, Jr., U.S. Pat. No. 3,715,797 to Jackson et al. and U.S. Pat. No. Re. 32,086 to Spirig, the disclosures of which are hereby incorporated by reference.
As indicated in the above patents, in use the solder wick is placed on the solder connection and heat is applied to the wick and/or the solder. The solder melts and is drawn up onto the wick by capillary forces.
Hood describes a braid of 40 A.W.G. gauge (about 0.0031" diameter) copper wire with strands in groups of four. The wick is braided from a machine having 16 heads so that the wick is 64 strands thick.
Spirig describes a wick of knitted construction comprising at least one strand of copper, wherein each strand has a diameter within the range of 0.1 mm to 0.25 mm (about 0.0039" to about 0.0097"). According to Spirig, with a copper strand of less than 0.1 mm diameter the knitting process may be too slow and there is a risk of strand breaks.
In the above-noted U.S. Pat. No. 3,627,191, Hood does suggest the use of strands of 44 gauge wire as a possible alternative in the construction of solder removal wicks. In this proposed alternative, however, the 44 gauge wire is braided "in 16 groups of six strands," for a total of 96 strands per braid. Applicant is aware of no commercial product which has been prepared in accordance with this alternative proposed in Hood. In practice, the lower limit for wire thickness in commercial products has been 42 gauge wire (about 0.0025" diameter).
A particular problem presented with the available soldering wicks relates to their relatively substantial width dimensions, which is a function of several factors including the gauge of the wire and the number of strands employed. A proper braid size must be utilized in any given solder removal operation in order to optimize the removal effect. Whereas a small braid used on a large connection does not remove all of the solder, a large braid on a small connection may remove too much. In particular, the available soldering wicks have all been too wide for use in the desoldering of so-called surface mount devices, which employ very thin leads (typically, 0.005 to 0.010") spaced relatively closely to one another. Thus, conventional wicks of standard width generally bridge 2-5 leads of a typical surface mount device at a time. This makes selective desoldering of any one of these leads extremely difficult, if not impossible, without bridging to additional leads.
A further problem presented with the prior art wicks relates to the generation of excessive heat when the wick and/or solder is brought into contact with a soldering gun and the solder is melted. If the molten solder is not picked up quickly by the wick, substantial quantities of heat can be introduced into the body of a device with which the leads being desoldered are associated. In particular, many devices comprising frames or other elements of synthetic plastic materials may suffer serious damage during the course of desoldering operations, if the molten solder is not removed rapidly.
One approach to reducing the amount of heating time required to raise the wick to a sufficiently high temperature to result in the melting of the solder is to reduce the amount of copper in the wick. For example, Spirig suggests the use of an open-mesh structure prepared by "weaving, stranding, braiding, knitting or crochetting"; the preferred process involves the use of a knitting machine, which results in the aforementioned lower wire diameter limit of 0.1 mm. Moreover, to the best of applicant's knowledge, a product with a diameter approaching the lower width limit of 2 mm (about 0.078") and having an open mesh structure as proposed by Spirig has not been commercially available. In any event, it is not believed that a product comprising a limited number of strands of an extremely thin wire could be prepared using a knitting process of the type described by Spirig on a commercial scale.
The most commonly available type of wick has been of the braided variety, comprising a plurality of wires braided together to form a hollow tube, which is subsequently flattened to provide the final product. Such wicks are prepared using various types of braiding equipment which are well known in the art. For preparation of the braided soldering wicks as described, for example, in Hood, an exemplary system is available under the designation 12 Carrier "Wardwellian" Rapid Braider from Wardwell Braiding Machine Company, Central Falls, R.I. Such braiding machines are also available equipped with 16 and 24 braid ribbon carriers.
While the available braiding machines have proved generally suitable for preparation of desoldering wicks using wires of a substantial gauge (e.g., the 40 gauge wire employed according to Hood), such apparatus has not been suitable for use in the preparation of products comprising thinner wires (for example, 44 gauge). In particular, substantial breakage of the thinner gauge wire during the braiding operation has prevented the introduction of wicks comprising a limited number of strands (e.g., three) of relatively thin (e.g., 44 gauge) wire as would be suitable for use in desoldering operations involving thin or closely-spaced leads.
It is an object of the present invention to provide a desoldering wick which is suitable for use in desoldering operations where a rapid removal of solder from thin or closely-spaced leads is necessary to prevent potential damage to associated equipment.
It is a further object of the invention to provide methods and apparatus which are suitable for the manufacture of such desoldering wicks.